Well, I don't really know too much about this. Evidently in men, excessive (whatever that means) masturbation can cause a rise in testosterone with a corresponding rise in DHT. But, the genetics have to be there for this to happen so ...

The thing to do would be to try Propecia ( Finasteride - Wikipedia, the free encyclopedia ) If it is from a build-up of DHT, then Propecia would stop the hair loss.

The thing to keep in mind though is that if it really is masturbation causing DHT buildup, then the genetics for hair loss were already there and just accelerated by that DHT increase. It is/was going to happen anyway. If the Propecia doesn't have any effect, then it's not DHT.

Did the doctor consider something as simple as stress? How are your stress levels? That can cause hair loss as well.